Kiel 2011 – scientific programme

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P: Fachverband Plasmaphysik

P 3: Umwelttechnik / Mikroplasmen / Diagnostik

P 3.6: Talk

Tuesday, March 29, 2011, 12:15–12:30, HS H

Determination of electron densities by diode-laser absorption spectroscopy — •Yusuf Celik¹, Tsanko Tsankov¹, Dirk Luggenhölscher¹, Uwe Czarnetzki¹, and Mitsutoshi Aramaki² — ¹Institute for Plasma and Atomic Physics, Ruhr -University Bochum, Germany — ²Department of Electrical Engineering and Computer Science, Nagoya University, Japan

A novel method to determine electron densities in pulsed low pressure ICP discharges via absorption spectroscopy on argon metastables is presented. The laser system used in the experiment is an external cavity diode laser (ECDL) in Littrow configuration tuned at a vacuum wavelength of 696.73 nm. The temporal evolution of the line-integrated absorption from metastable argon atoms in the Ar1s5 (Paschen notation) state in the afterglow is recorded. An analytical expression for the decay of metastables is presented which allows the determination of electron densities. For the analysis, the spatial metastable and electron density profile inside the chamber and the line-integration of the detected signal is taken into account. Further, the analytical model and a developed 2D fluid-dynamic simulation show that the metastable density distribution is spatially homogeneous. The results for electron densities obtained with this technique are compared to Langmuir probe measurements showing good agreement. Furthermore, metastable densities and gas temperatures are determined in the stationary plasma by scanning the laser wavelength over the Doppler-shaped absorption profile.